The subject matter disclosed herein relates to a thermal valve and, more particularly, to a thermal valve including an elastic element formed of memory metal alloy (elastic MMA).
In various applications, such as the automotive and aircraft industries, thermal valves are commonly installed in inlet or outlet ports of heat exchangers where header tanks connect the inlet and outlet ports of a fluid stream. The valves serve to balance the flow between the inlet and the outlet ports connecting the headers and the heat exchanger core headers, thereby maintaining required fluid temperatures and pressures. To this end, the valves generally incorporate a heat and/or pressure relief mechanism whereby, if the system heat or pressure reaches a critical point, the valve allows fluid to bypass the heat exchanger core to prevent, for example, over pressurisation in the heat exchanger core and potential damage.
Currently, the heat release mechanism of typical thermal valves relies on wax extension technology using either a flat elastomer diaphragm or an elastomer bag. In the case of the elastomer bag, as the wax heats, it expands and exerts a force on the elastomer bag and a piston assembly coupled to the bag to close the valve. By contrast, as the wax cools, it contracts and causes the piston assembly to return to its initial position.
In practice, it has been observed that wax extension technology presents certain drawbacks. In particular, the wax tends to lose its memory after a given number of thermal cycles. Also, wax tends to have a slow thermal response characteristic, which makes the timing of the thermal valves difficult to manage. Further, wax extension technology requires structural elements for containing the wax so that wax and oil contamination can be avoided.